This type of technique is conventionally known as for example a rotor disclosed in Patent document 1 listed below. This rotor includes a rotor core, a shaft hole (a shaft-fastening hole) provided at the center of the rotor core, a rotary shaft (a rotor shaft) inserted in the shaft-fastening hole by interference fit, through holes formed to prevent magnetic flux leakage on both wing portions of the rotor core, rectangular slots formed in separate right and left slots between the through holes to leave a central portion of the rotor core, rectangular field permanent magnets fitted in the slots, salient poles portion formed above the permanent magnets, and bridges to connect the salient poles and the rotor core between the slots.
Herein, a plurality of nearly arc-shaped slits are formed between the through holes and the shaft-fastening hole. It is configured such that the thickness in a radial direction between the inner circumference of each slit and the shaft-fastening hole is equal to the thickness in the radial direction between the inner circumference of each slot and the shaft-fastening hole. Accordingly, when the rotor used in the motor is rotated at high speeds, deformation of the rotor core due to interference fit between the shaft-fastening hole and the rotor shaft is reduced by those slits. This reduces concentration of stress on thin portions.